Treatment of bituminous sands



Jan. 12, 1960 J. E. SHERBORNE 1,

TREATMENT OF BITUMINOUS SANDS Filed July 19. 1957 2 Sheets-Sheet 1 /VVi47dl JOHN E. SHEREOR/VE imam 5% Jan. 12, 1960 J. E. SHERBORNE 2,921,010

TREATMENT OF BITUMINOUS SANDS United States Patent 2,921,010 TREATMENTOF BITUMINOUS SANDS John E. Sherborne, Whittier, Calif., assignor toUnion Oil Company of California, Los Angeles, Calif., a corporation ofCalifornia Application July 19, 1957, Serial No. 672,977

7 Claims. (Cl. 208-41) This invention relates to the recovery ofhydrocarbons from hydrocarbon-containing solids such as tar sand,oilsoaked diatomite, and the like. This invention particularly relatesto an improved process and apparatus for treating such materials atrelatively low temperatures utilizing particularly efficient sandwashing and separation steps to efiect a substantially complete recoveryof the hydrocarbon material present.

Extensive deposits of tar sands or bituminous sands are known to existat widely separated places in the world. These materials are essentiallya silicious material, such as sands, loosely agglomerated sandstones, ordiatomaceous earth, saturated with relatively heavy or viscoushydrocarbon materials resembling low gravity crude petroleum. They existnear the surface of the earth and are generally discovered throughlocation of their outcroppings. Extensive deposits of such materialshave been discovered in the Athabaska region of northern Alberta,Canada, in the Uinta Basin near Vernal in north- Sisquoc River Valley,near Casmalia, and elsewhere.

Surveys of these deposits have revealed that they contain tremendousquantities of hydrocarbon materials very similar to low gravity crudepetroleum and individual deposits have been estimated to contain of theorder of 60 to 70 million barrels of tar sand oil. Extensive recovery ofthese oils has not been achieved, primarily because of the expense inrelation to crude petroleum in spite of the fact of the accessibility ofthe material near the earths surface. However with rising costs of crudepetroleum due to production and depletion of known petroleum reserves,an efficient and economical process and apparatus for the treatment ofsuch bituminous sands has become highly desirable. V p

The principal disadvantage in previous tar sand recovery processes liesin the extensive requirement of chemical reagents and in the difficultyof separating the very heavy oil from the sand or other solid grainsafter the pulping or treating step. The present invention successfullyovercomes these disadvantages through the utilization of a particularlyeflicient method oftreating the pulped material to efiect sandseparation while avoiding oil rewetting.

In the following description the phrases bituminous sand,or tar sand areused to refer generally to all granular solid bituminous orpetroliferous materials soaked with a usually highly viscous liquid orsemi-liquid hydrocarbonaceous material, although it specifically refersto a characteristic type of bituminous solid consisting of discreteparticles of sand bound together by a continuous viscous hydrocarbon oilphase. This terminology is used for the sake of simplicity ofdescription, and it should be understood that the process and apparatusherein described may be applied to other solids similarly containing abituminous or viscous hydrocarbonaceous coating.

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v The present invention is directed to a low temperature process using awarm aqueous solution of a special alkali metal silicate, with orwithout other reagents, and a moderately heavy hydrocarbon diluent toseparate the heavy oil from the bituminous sands, and in which processspecial procedurm and apparatus are used in handling the efiluent fromthe mixing step in which these materials are agitated with one anotherto effect the separation of the heavy oil from the sand.

It is a primary object of this invention to provide an improved processfor the separation and recovery of heavy oil from bituminous solids suchas tar sand and the like.

It is a specific object of this invention to provide a particular stepfor treating the oil and water stream which flows from the pulper afterremoval of most of the solid material whereby a substantially completeseparation of fine solids and silt is eifected simultaneously from boththe aqueous and the hydrocarbon phase.

It is a further object of this invention to provide an improvedapparatus adapted to eifect the foregoing objects.

Other objects and advantages of this invention will become apparent tothose skilled in the art as the description and illustration thereofproceed.

Briefly, the present invention comprises, in its preferred modification,the mining of surface or near-surface deposits of tar sand and the likeby the usual procedures to produce a raw feed material consisting ofchunks or pieces of tar sand of the order of 15 inches in averagedimension. Smaller sizes digest more rapidly, but the sizes may belarger in some cases. This may be done by open pit mining in whichoverburden is stripped away and the tar sand is mined by means ofbulldozers, clam shell shovels, and similar equipment. Drilling andblasting may also assist in the breaking up of the tar sand into theaforementioned sized particles. The mined material is transferred to afeed hopper which controls the rate of flow to a mixer. Here it is mixedand pulped with an aqueous sodium silicate solution and a hydrocarbonsolvent at a slightly elevated temperature. This mixing continues for aperiod of between about 0.2 and about 2.0 hours and at a temperature ofbetween about F. and about 250 F. Preferably this mixer is of the rotarykiln type with internal baflles and conveyor flights so as to controlthe residence time of the material in the mixer. This treatment reducesthe tar sand chunks to a heavy slurry of sand, water, and oil. 1

The efiluent from the mixer or pulper is a slurry or pulp of treatedsand, aqueous chemical solution, and a hydrocarbon phase which includesthe separated bitumen and the relatively light diluent oil. This slurryor pulp is discharged immediately to a primary separation zone in whicha very rapid separation of the treated solids is eifected. This leaves astream of fluid including the hydrocarbon and aqueous phases. Sincethere is a considerable quantity of sand present at all times in thisprocessing step, it is essential that some slight sand agitation' beelfected in order to liberate residual oil droplets which are trapped inthe downwardly progressing sand during the dropout of the sand grainsfrom the fluid phases. The sand is discharged at the bottom of theprimary separator into a washer-drier in which a considerable quantityof the water present in the sand stream is recovered for recirculation.If desired, makeup water to the process may be added at this point torecover residual silicate solution from the sand as well.

From the top of the primary separator are discharged the aqueous andhydrocarbon phases substantially free of sand grains, but containingvariable amounts of very fine solids such as silt and clay. In theseparator-thickener zone, to which these phases flow, a substantially Qcomplete removal of these silt-like solids is effected from the aqueousphase and a clean water stream is produced for recirculation; Asubstantially dry oil phase is dis charged from the thickener into asettling zone, such as a wash tank, if desired, to complete removal oftraces of water. This is an optional step in this invention. Otherwise,the; oil product is essentially water and silt free, being a dilutemixture of hydrocarbon diluent and the relatively heavy hydrocarbon orbitumen separated from the sand in the process. This oil phase is atsome point treated as by distillation to recover the diluent oil forrecirculation to the pulper. From the bottom of the thickener zone isremoved a concentrated slurry of silt and water which is discharged tooutdoor settling basins.

As illustrated by the following examples and as described herein, thespecific steps taken in the separator and settling zones to preventcontact er the sand with separated oil have been found tobe extremelyimportant in the successful recovery of up to 99.9% of these heavy oilsand in the production of clean sand containing less than 0.10% of theoriginal oil.

The process of the present invention is best described and illustratedby reference to the accompanying drawings in which: 7

Figure '1 is a schematic flow diagram showing portions of the apparatusin elevation view, and

v Figure 2 is an elevation view in cross section showing the details ofthe thickening zone into which the oil and aqueous efiiuent from theprimary separator zone is discharged for complete separation of theaqueous, hydrocarbon, and silt phases.

Referring now more particularly to Figure 1, the essential equipmentelements employed in the process and" apparatus of the present inventioninclude pulper or mixer primaryseparator 1 2, sand washer and drier 14,and thickener 161. Arr optional oil producfstorage-settler'18 may beused if desired. The subsequent discussion of me invention in connectionwith Figure 1 will be conducted as a typical example of the process andapparatusof this invention applied to the treatment of Sisquocbituminous sand at a; rate of approximately 200 tons per day. Althoughthe tar sand may contain between 20 and 40 gallons of oil per ton andhavea gravity from'2 to 10 API; a typical bituminous sand contains about30 gallons per ton of 4 API gravity bitumen.

The freshly mined bituminous sand is introduced into pulper 10 by meansof conveyor 20 at a rate of 200 t./d.' (tons per day) controlled bysolids feeder 21. A light coker gas-oil as diluent oil is introduced ata rate of 191 b./d. (barrels per day) and a temperature of 180 F.through line 22 at a rate controlled by valve 24. Also introduced intothe pulper is an aqueous alkali metal silicate solution, with or withoutother reagents, which flows through line 26 at a rate of 286 b./d.controlled by valve 28. This material is maintained at a temperature ofabout 180 F. by means of heater or exchanger 30. To maintain a pulpertemperature of about 180 F. within pulper 10, steam at the rate of 482pounds per hour is also introduced through line 32 at a rate controlledby. valve 34.

The relative rates of the foregoing ingredients introduced into pulpingzone 10 are specific to one typical operation. tainedwithin certainlimits in order to effect the most rapid and efficient liberation of thebituminous material from the sand or other solid grains. Pursuant tothis the diluent hydrocarbon rate is that suthcient to produce anoilphase having an APIgravity above 10, and is preferably maintainedbetween limits of. about 0.1 and about 2.5 b./ t. (barrels per ton) ofraw bituminous sand feed. The aqueous silicate solution is introduced ata rate maintained between about 0.75 and about 5.0 b./ t. of raw sandfeed, and preferably between about 1.0 and 1.5 b./ t. This aqueous.solution contains between about 0.5 and 20, and preferably between about0.75 and about 10.0 pounds of In general however they are preferablymain an aqueous sodium silicate concentrate per barrel. This concentrateis a 34% by weight aqueous solution and is a special material marketedcommercially under the name Silicate 120. It has a Na O to SiO ratio ofabout 0.55 mol per mol. Other high basicity sodium silicates may besubstituted provided this'ra'tio' is above about 0.4 and preferablygreater than about 0.5. The' commercial water glass of commerce is notsatisfactory since it has a ratio of about 0.25.

The pulping temperature must be maintained higher than about F. andpreferably is maintained above 180 F., although it ordinarily should notrun above about 250 F. The operation of the pulping zone is controlledrelative to the set rate and thesize of the pulper so that the rawbituminous sand is subjected to the action of steam, the aqueoussilicate, and the hydrocarbon diluent within the pulping zone foraperiod of between about 0.1.and 2.0 hours. Under the conditions givenpreviously a pulping time of about 0.25 hour will liberate substantiallyall of the bitumen from the sand and produce a spent sand containingless than about 3 pounds of hydrocarbon per ton.

The discharge end of pulping zone 10 is provided with trash screen 36 bymeans of which rocks and nondisaggregated lumps of tar sand aredischarged from the system by means of conveyor 38. The fluid pulpdischarges through the screen 36 and flows by meansv of line 40 into thetop of primary separation zone 12.. This stream contains approximately58 t./ d. of water, 55 t./d. of oil, and 172 t./d. of sand. Primaryseparation zone 12 operates at a temperature a few degrees below that ofthe pulper. This is attained by making line 40 as short as possible andproviding for the immediate transfer of the pulp from the pulper intothe primary separator. Pref-- erably line 40 is an inclined pipe having.a slope of not less than 60 relative to the horizontal.

The interior of primary separation zone 12 is provided with a pluralityof baflies-42 over which the settling sand progresses in sequence toprovide the gentle agitation necessary to liberate mechanically trappedoil drops from the sand stream. If desired additional agitation may beprovided by introducing fluid such as recycle silicate solution into thebottom of primary separation zone 12 through line 44 at a ratecontrolled by valve 46.

From the bottom of primary separation zone 12 the treated sanddischarges through line 48 at a rate controlled by valve 50, which maybe a density valve responsive to the density of the sand water slurrycollecting in the bottom of primary separation zone 12. In any event,the sand discharges at a rate of 172 t./d. into washer 14 along with 193b./d. of water. The sand is picked up and conveyed upwardly by means ofconveyor 52 whereby a gravity separation of the aqueous phase isprovided. Preferably part or all of the make up water to the system isintroduced by means of line 54 controlled by valve 56 as wash water tothe washer-drier. The clean, oil-free sand is discharged fromwasher-drier 14 by means of line 58 and is conveyed to a suitabledisposal point.

The aqueous phase removed with the sand from the primary separation zone12 is separated from washerdrier 14 through line 60 and is dischargedinto the central well 62 of thickening zone 16. This stream flows atabout 160 F. at a rate of about 1168 b./d., containing about 5 t./d. ofsand and 1 b./d. of oil.

The overflow of oil and water from primary separator zone 12 passesthrough line 86 also into central well 62 of thickener 16. This streamflows at a rate of about 1081 b./d. and includes 754 b./d. of water, 327b./d. of oil and 12 t./d. of silt and sand. The temperature of thestream is about F.

Thickener 16 is an essential cylindrical vessel provided internally witha coaxial central well 62 into which all of the fluids for treatment areintroduced. In thickener 16 a complete separation of silt-like solidsfrom the oil and aqueousphases, andthe oil and aqueous phases from eachother are effected. The floor of thickener 16 is provided with apluralityof radial rake-arms 64 rotated by means of a vertical centralshaft hr by other means, driven by rotating means 68. In the presentexample the central well is such that the fluid residence time is about12 hours devoted to the settling of silt from the oil phase as well asthe separation of the oil and water phases. The annular volume outsidewell 62 is sized to give a water residence time of about 6.0 hoursduring which time substantially all of the silt settles from the aqueousphase. Rake arms 64 are provided with rakes inclined at such an angle sothat rotation of the rakes move the settled silt as a thickened sludgeradially inward toward silt outlet 70. The thickened silt isv removedthrough line 70 at a rate controlled by valve 72, the silt concentratecontaining about 87 b./d. of water and 17.0 t./d. of solids.

The clear water effluent is removed from collector 74 surrounding theupper periphery of thickener 16 by means of line 76 at a rate of 1821b./ d. This material actually constitutes the aqueous silicate solutionto which make up aqueous silicate concentrate is introduced by means ofline 78 at a rate of 2.5 gallons per hour controlled by valve 80. Freshwater is introduced by means of line 82 at a rate of about 355 b./d.controlled by valve 84. This may, if desired, flow into the clear,aqueous stream in line 76. As previously indicated this is preferablyemployed, wholly or in part, as wash water for the spent sand and isintroduced through line 54 previously described. The total aqueousstream from thickener 16 continues through heat exchanger 30 where it isheated to about 180 F. and is introduced into pulping zone through line26 as previously stated.

In central well 62 broken line 90 indicates the approximate position ofthe oil emulsion-aqueous phase interface. This is maintained at adistance about two-thirds of the way down in the central well. Theaqueous streams flowing through lines 60 and 88 from washerdrier 14 andthe optional settling zone 18 respectively are introduced below thislevel because they contain only slight quantities of oil. The primaryseparator efiluent flowing through line 86 and containing about 30% byvolume of oil is introduced above level 90 into the supernatant phaseconsisting of separated oil and possibly a layer of oil-water emulsion.Preferably the interface denoted byline 90 is detected and the rate ofremoval of the supernatant water and silt-free oil phase from weir box92 or other removal means is controlled so as to maintain asubstantially constant position of the interface. In any event, theresidence time for the oil phase is approximately 12 hours, during whichtime the silt and water settle out. The oil stream is removed from weirbox 92 through line 94 at a rate controlled by valve 96 or other means.The temperature of this stream is approximately 168 F., it flows at arate of 328 b./d. of oil, and contains only traces of sand and water.

This essentially dry silt-free oil stream may be "discharged intooptional storage zone 18 by means of distributor 98 disposed in thelower portion of the vessel. Any separated traces of the aqueous phaseare removed from the bottom of settling zone 18 through line 88 and maycontain a trace of solids. Heating coil104 is provided within settlingzone 18. The dry oil'is removed from the top of settling zone 18 bymeans of take-on weir 100.

This oil stream is pumped by means of a pump not shown from weir 100when tank 18 is employed, or otherwise directly from line 94 into andthrough line 102 to distillation facilities which may be located atthe'plant site or at a remote area where it is associated with refiningfacilities for treating the recovered oil. This stream flows at atemperature of about 153 F. and contains 328 b./d. of oil and onlytraces of water and solids. The etfluent dry oil is heated in exchangermeans 106. and

is distilled in distillation column 108. A stripping gas such as steamis introduced in'to'the bottom of distillation column 108 throughline110 at a'rate controlled by valve 112. The overhead vapor flowingthrough line 118 from still 108 is condensed in condenser 120, part ofthe condensate is returned through line 122 as reflux, and the remainderis pumped by means of a pump not shown through line 22 into pulping zone10. The stripped diluent oil-free bitumen is removed through line 114 ata rate of 137 b./d. controlled by valve 116.

This product oil has the following properties:

By means of the above described process, bituminous sands are readilytreated to effect better than 96% by volume of the bitumen containedtherein at moderate temperatures and pressures and with only slightconsumption of chemicals. The sand discharged from the system con tainsless than 5 pounds per ton of residual oil.

Referring now more particularly to Figure 2, an enlarged detailed viewof thickener 16 shown in Figure 1 is here shown in partial crosssection. It comprises an inner stratification zone contained in centralwell 62 and a clarification zone 63 surrounding it. Overflow weir box 74extends around at least part of the upper periphery of the clarificationzone. Drive means68 of Figure 1 is shown consisting of an electric motor130, and a reduction gear 132 from which central shaft 66 runsdownwardly to connect to radial rake arms 64.

Concrete foundation 134'is provided with a tunnel 136 through whichoutlet line 70 passes from a central connection at the bottom of vessel.16. This tunnel permits the bottom of the thickener to be opened ifnecessary and the accumulated silt discharged with the aid of jets ofwater.

Central well 62 is positioned coaxially within vessel 16 and iscontainedwithin cylindrical section 138 which extends downwardly fromthe roof of vessel 16 a distance equal to between about 50% and 90% ofthe vessel height. A weir box 140 provided with a variable weir 142 isprovided at the upper edge of central well 62. A weir activator 144which in turn is actuated by dilferential liquid level controller 146 isprovided. The controller is responsive to water-oil interface detector148.

Oil outlet line 94 opens downwardly from the bottom of Weir box f0r thedischarge of the dry and silt-free oil collected in central well 62.

Line 86 leading from the top of primary separator 12 and provided withvalve 150, opens downwardly into the top of thickener 16 within centralwell 62 and terminates in a distributor 152 if desired, but in any eventlocated at v a point above interface 154. This is the eifluent from theprimary separator and contains a substantial quantity of oil. Byintroducing it at a point aboveinterface 154, a residence time of about12 hours is provided wherein the water and silt drop out substantiallycompletely and pass downwardly through interface 154 and with theaqueous phase into the surrounding body of water in the separator.

Distributor 156 is provided within central well 62 at a point belowinterface 154. This distributes the essentially aqueous streamcontaining silt and which also may contain some oil. This stream is thesand washer-drier efiluent which is introduced through line 60.Optionally an aqueous stream from the storage zone 18 discharges throughline 88. If desired, these may be introduced into central well 62 bymeans of separate lines if desired and each may be provided with its owndistributor. In any 7 event, any aqueous silt-containing streams whichalso may contain minor amounts of oil are introduced below interface154, while the essentially oily streams containing substantialquantities of oil together with silt and solids are introduced aboveinterface 154.

The lower interface 154is continuously .detected by means of element 148and the maintenance of'this interfacial position prevents the flow ofoil frorrrcentral Well 62 outwardly aroundthe periphery of cylindricalsection 138 into the surroundingv aqueous body of fluid in separator 16.With sufiicientresidence time in central well 62, of 12 hours in thiscase,*the oil overflow through line 94 is dry silt-freeoil. Similarly asuflicient residence time of about 20 hours produces silt-free aqueoussilicate solution from the'upper periphery of the annular shapedsurrounding volume of water in separator 16.

' The purpose of central well '62 is essentially three-fold: first, toseparate substantially all of the silt and solids from the oil phase,second, to separate the oil phase completely from the aqueous phase, andthird, to prevent excessive contactof the oil with airin order to avoiddegradation of this highly reactive oil. The surrounding annular spacein thickener 16 is purely to provide settling time for the aqueoussilicate phase in order to remove silt and other solids therefrom. Theaqueous phase discharges centrally at the bottom of thickener 16 andflows slowly upwardly to the upper peripheral water drawoff 74. Ampletime is thus provided for the gravitational settling of thesilt andother solids. vAs stated previously the clear aqueous phase overflowdischarges through line 76 while the settled silt is thickened andformsa heavyslurry which is moved radially inward by rakes 64 to thecentral silt outlet line 70.

In the experimental verification of the process of this invention, 200vt./d. of Sisquoc bituminous sand were treated according to' the processdescribed. in Figure 1. The thickener was a vessel 20 feet in height and30 feet in diameter. The central well was 15 feet in height and 8 feetin diameter and interface 154 was detected and maintained at a point 12-feet from the top of the vessel. The residence time for the oil phasewas approximately 12 hours at a liquid feed rate into the thickenerequal to those given in the description of Figure 1. The totalthickener-feed was 415 t./d. or 2408 b./d. including 329 b./d. of-oil,1989 b./d.- of-water, and 17.0 t./d. of silt and solids. The clear watereffluent from. the thickener amounted to 1902 b./d.- with a negligiblequantity of oil and silt. The silt concentrate was composed of 87 b./ d.of water and 17 t./d. of solids. The oil overflow from the'central wellcontained 328 b./d. of .oil, withonly traces of water or silt andsolids.

The operating conditions must be Varied somewhat to handle mixturescontaining silt of varioussizes, the finer sizes taking longer tosettle. Accordingly in the central well where the oil is freed of waterandsilt, residence times of from 5.0 to 25 hours and preferably fromabout 10 to 20 hours for the oilare contemplated. The well should besized to maintain upward oil velocities .on the order of 0.1 to 5.0 feetper hour, and preferably from about :25 to"2.0 feetgper hour. In thesurrounding annular water-settling zone, water residence times of from1.0 to 20'hours and preferably between about 2 to about hours arecontemplated. The annular zone should be sized so as .to give upwardwater velocities of between 0.1 and 10.0 feet per hour, andpreferablybetween about 0.5 and about 4.0 feet per hour.

A particular embodiment of the present invention has been hereinabovedescribed in considerable .detail by way of illustration. It should beunderstood that various other'modifications and'adaptations thereof maybe made by those-skilled in this particular 'art without departingfrom-the spirit and scope'of'this invention asset forth in the appendedclaims.

- I claim:

1. In a process for the recovery of hydrocarbon values fromnaturally-occurring hydrocarbonaceous mineral solids wherein saidsolidszare agitated in a pulping zone withaqueous sodium silicate and aliquid hydrocarbon diluent at a moderately elevated temperature for aperiod of time suflicient to form. a substantiallyhomogeneous fluidpulp, and said pulp isthereafter treated to separate therefrom ahydrocarbon phase, an aqueous phase, and essentially oil-freesolids,.the method of effecting said separation which comprises: (1)introducing said pulp into the upper end .ofa-vertically elongatedprimary separation zone; (2) .allowing .the solids components of saidpulpv to descend by gravity through said separation zone to the lowerend thereof; (3) passing a stream of aqueous sodium silicateupwardly'through said separation zone in intimate countercurrentcontactwith thedescending solids therein; (4) withdrawing a liquid phasecomprising hydrocarbons and aqueous sodium silicate from the upper endof said separation zone; (5) removing de-oiled solids from'the lower endof said separation zone; (6) washing said de-oiled solids with water toobtain substantially oil-free-solids and a wash liquor comprising water,silt, and hydrocarbons; (7) introducing said wash liquor into the lowerpart of a stratification zone which opens downwardly into a surroundingclarification zone; (8) introducing the liquid phase obtained in step.(4) into the upper part of said Stratification zone; (9) maintainingthe liquid within said stratification zone in a quiescent state, wherebyit separates into an upper hydrocarbon phaseand a lower aqueous phase;(10) withdrawing said upper hydrocarbon phase from the upper end of saidstratification zone and withdrawing said lower aqueous phase fromtheupper end of said clarification zone at such rates, relative .to eachother, that the interface between said phases is maintained at a levelbetween the levels at which the said liquid phase and said wash liquorare introduced into said clarification zone; and (11) Withdrawing athickened slurry of silt from the bottom of said clarification zone.

2. A process as defined by claim 1 wherein the said sodium silicatesolution contains between about 0.5.and about 20 pounds per barrel of a34 percent by weight aqueous concentrate of sodium silicate having a NaO/SiO ratio greater than about 0.4.

3. A process as defined by claim 2 wherein between about 0.75 and about5 .0 barrels of said aqueous sodium silicate and between about 0.1 andabout 25 barrels of said hydrocarbon diluent are employed per ton ofsaid hydrocarbonaceous solids.

4. A process according to claim 1 wherein in step (10), the rate atwhich said upper hydrocarbon phase is withdrawn from said stratificationzone is so controlled relative to the volume of said zone and the rateat which hydrocarbons are introduced thereinto that the upward linealvelocity of hydrocarbons within said zone is between about 0.25 andabout 2.0 feet per hour, and the residence time of hydrocarbons withinsaid zone is between about 10 and about 20 hours.

5. A process according to claim 1 wherein in step (10) the rate at whichsaid lower aqueous phase is withdrawn from said clarification zone is socontrolled relative to the volume of said zoneand the rate at whichaqueous liquid is introduced thereinto that the upward lineal velocityof aqueous liquid within said zone is between about 0.5 and about 4.0.feet per hour, and the residence time of aqueous liquid. within-saidzone is between about 2 and about 10 hours.

6. A process as.defined by claim 1 in combination with the steps ofintroducing the hydrocarbon phase which is withdrawn from saidstratification zone into a final settling zone; withdrawing settledwater from the bottom of said settling. zone; and introducing said waterinto said Stratification zone at a level below that of said interface.

7.' A process asdefined byclaim 1. wherein the aqueous phase withdrawnfrom said clarification zone is introduced into said pulping zone assaid aqueous sodium silicate.

References Cited in the file of this patent UNITED STATES PATENTSHarrington Feb. 25, 1941 Streppel June 10, 1924 Arveson Dec. 1, 1942

1. IN A PROCESS FOR THE RECOVERY OF HYDROCARBON VALUES FROMNATURALLY-OCCURRING HYDROCARBONACEOUS MINERAL SOLIDS WHEREIN SAID SOLIDSARE AGITATED IN A PULPING ZONE WITH AQUEOUS SODIUM SILICATE AND A LIQUIDHYDROCARBON DILUENT AT A MODERATELY ELEVATED TEMPERATURE FOR A PERIOD OFTIME SUFFICIENT TO FORM A SUBSTANTIALLY HOMOGENEOUS FLUID PULP, AND SAIDPULP IS THEREAFTER TREATED TO SEPARATE THEREFROM A HYDROCARBON PHASE, ANAQUEOUS PHASE, AND ESSENTIALLY OIL-FREE SOLIDS, THE METHOD OF EFFECTINGSAID SEPARATION WHICH COMPRISES: (1) INTRODUCING SAID PULP INTO THEUPPER END OF A VERTICALLY ELONGATED PRIMARY SEPARATION ZONE, (2)ALLOWING THE SOLIDS COMPONENTS OF SAID PULP TO DESCEND BY GRAVITYTHROUGH SAID SEPARATION ZONE TO THE LOWER END THEREOF, (3) PASSING ASTREAM OF AQUEOUS SODIUM SILICATE UPWARDLY THROUGH SAID SEPARATION ZONEIN INTIMATE COUNTERCURRENT CONTACT WITH THE DESCENDING SOLIDS THEREIN,(4) WITHDRAWING A LIQUID PHASE COMPRISING HYDROCARBONS AND AQUEOUSSODIUM SILICATE FROM THE UPPER END OF SAID SEPARATION ZONE, (5) REMOVINGDE-OILED SOLIDS FROM THE LOWER END OF SAID SEPARATION ZONE, (6) WASHINGSAID DE-OILED SOLIDS WITH WATER TO OBTAIN SUBSTANTIALLY OIL-FREE SOLIDSAND A WASH LIQUOR COMPRISING WATER, SILT, AND HYDROCARBONS, (7)INTRODUCING SAID WASH LIQUOR INTO THE LOWER PART OF A STRATIFICATIONZONE WHICH OPENS DOWNWARDLY INTO A SURROUNDING CLARIFICATION ZONE, (8)INTRODUCING THE LIQUID PHASE OBTAINED IN STEP (4) INTO THE UPPER PART OFSAID STRATIFICATION ZONE, (9) MAINTAING THE LIQUID WITHIN SAIDSTRATIFICATION ZONE IN A QUIESCENT STATE, WHEREBY IS SEPARATES INTO ANUPPER HYDROCARBON PHASE AND A LOWER AQUEOUS PHASE, (10) WITHDRAWING SAIDUPPER HYDROCARBON PHASE FROM THE UPPER END OF SAID STRATIFICATION ZONEAND WITHDRAWING SAID LOWER AQUEOUS PHASE FROM THE UPPER END OF SAIDCLARIFICATION ZONE AT SUCH RATES, RELATIVE TO EACH OTHER, THAT THEINTERFACE BETWEEN SAID PHASES IS MAINTAINED AT A LEVEL BETWEEN THELEVELS AT WHICH THE SAID LIQUID PHASE AND SAID WASH LIQUOR AREINTRODUCED INTO SAID CLARIFICATION ZONE, AND (11) WITHDRAWING ATHICKENED SLURRY OF SILT FROM THE BOTTOM OF SAID CLARIFICATION ZONE.